Many printing systems accept a high-level description of the output in the form of a page description language (PDL) and convert the high-level description to a pixel-based representation, suitable for sending to a print engine. Examples of such printing systems include server-based raster image processors (RIPs) that send their output to a file or a printer. Other examples of such printing systems include standalone embedded printers and split systems where a portion of processing is performed in a driver or server, and the remaining processing is performed on a low-capability printer device.
One processing path for print data is for the print data to be converted from PDL format to a display list (DL) which contains drawing commands. The display list is then converted to one or more intermediate formats, before finally being rendered to pixels. An advantage of an intermediate format is that the intermediate format is significantly smaller than the pixel output, and yet still allows analysis and processing of page content.
Many print documents contain some content that is repeated over many pages. For example, corporate PowerPoint™ presentations often have common headers and footers repeated on each page. Another example is a mail-merged letter or brochure where content is substantially duplicated over multiple pages with only personal details being different. The overhead of repeated processing of the same content multiple times can lead to unnecessary reduction in performance.